Fuel Pump?

[kellydee]

I just went from a 96 merc 5.7 to a 2007 merc 5.7 carbed.The old motor had a mechanical fuel pump and the new one has an electric.Shouldn't the fuel pump kick on when the ign switch is on,or does it not come on until the switch is in the start position?Old motor had a 10 pin connector and the new one has a 14 pin.I got the 10to 14 pin adaptor plug.Shouldn't the harness already supply power to the pump?

 

[Reel Poor]

Re: Fuel Pump?

It only runs in the cranking position. Once the engine starts an oil pressure switch closes and starts running the pump continuously or until the engine is shut down. Loss of oil pressure will also shut the fuel pump down.

 

[kellydee]

Re: Fuel Pump?

OK then,I'll go ahead and hook the boat up to my truck,get it out of the shop doorway so I don't make a huge mess and I'll give it a whirl.I was gonna turn it over for the first time(new motor) last evening but,when I turned the key on and didn't see the fuel filter fill up I thought I might have another problem to work out and didn't really have the time.Also,I installed a fuel filter just out of the tank as I needed one in-line befor the fuel flow sensor.I used one of those glass ones with a changeable filter.Is this a no-no in a boat?Possible leak problem?I used the hand pump from the kicker motor to get some fuel sucked up in the filter.#1 I could not get it to suck fuel all the way so,not sure if the ball pump is working incorrectly or what,had to pump real hard and fast to get some fuel to the filter but never got it all the way to the kicker.Maybe because the water sep filter is new and empty too?I wouldn't think so,if the ball is working correctly,should hold enough suction on it to pump all the way right? #2 After a few seconds,I can see the fuel drain back down to the tank.Shouldn't the anti-siphon valve keep the fuel from draining back to the tank?Or is that just an anti-siphon and not also a backflow preventor?I would think that once the filter is full,it would stay that way.Other wise,every time I shut down the motor,it will have to pull the fuel all the way from the tank again.I understand there will still be enough fuel in the float bowl to start but,seems like once it's in the line it should stay there.

 

[Don S]

Re: Fuel Pump?

I turned the key on and didn't see the fuel filter fill up

You shouldn't be able to SEE a filter fill up. Any filters with a clear bowl used for gasoline are outboard filters and should NOT be used in an engine compartment. The clear plastic bowls will not pass the fire test.

Also,it's best to prime the engine fuel filter and pump before starting. On new engines, I always use an outboard tank with a squeeze bulb to fill the filter, pump and carb for the first time. Prevents those very expensive fuel pumps from running dry.

 

[kellydee]

Re: Fuel Pump?

Crap!I had that feeling about the filter AFTER I bought/installed it.Kind of like the new fuel lines I installed.NOT marine grade.Only about 1/2 the thickness.Guess I need to redo those.Question #1 What about the anti-siphon valve?Shouldn't it prevent the fuel from running back to the tank?#2 are the plastic semi-transparent filters not ok either then?Should I find a metal one?#3 There was previously no filter between the tank and the water sep filter(unnessesary, I know)but,I installed a fuel flow sensor(Lowrance)and it requires a filter before it.Rather than cutting the steel tube comeing out of the water sep filter,I installed a filter just out of the tank.Is there a rule of thumb as to how long the line should/should not be between the tank and the pump?

 

[kellydee]

Re: Fuel Pump?

Just wanted to get back to the top of the page so I'm not getting missed.I've gotta leave soon to pick up work and was hopeing to pick up parts while I'm out since most marine stores are about 15-20 miles from home.Thanks,Jerry

 

[Don S]

Re: Fuel Pump?

#1 What about the anti-siphon valve?Shouldn't it prevent the fuel from running back to the tank?

That's not it's purpose, but it should. May have dirt in it, or the spring is broke causing the ball not to seat.

#2 are the plastic semi-transparent filters not ok either then?Should I find a metal one?

Nope, they are usually for outboards also. They do make metal inline filters with metal housings, but what I do is just install a second water seperating fuel filter in front of the fuel flow sender.

 

[kellydee]

Re: Fuel Pump?

Thanks again Don.What about the distance between the tank and the pump?Stay within certain distance or just keep it as short as I can?Originally only 18 inches but,adding another filter and FF sensor (which is supposed to be installed vertically)it's more like 4-5 feet to allow the filter and FF sensor to be mounted rather than hanging.

 

[Destin]

Re: Fuel Pump?

Make sure you get type A1 marine fuel hose. It is the only type approved for use in an enclosed engine compartment.
Download and save the revised (Nov 2003) fuel system regulations.

http://www.uscgboating.org/safety/boatbuilder/downloads/FUELSYSTEM.pdf

 

[sixholdens]

Re: Fuel Pump?

Just a quick note about electric fuel pumps.
When starting the motor, there is a bypass circuit to power the pump before the oil pressure switch takes over the job of providing power. Page 29 of the Boat Builders Handbook, 183.524, shows the circuit coming off the starter selonoid terminal of the ingnition switch, going to the oil pressure switch and then to the fuel pump. The oil pressure switch is a single pole, doulbe throw type switch, just means that you have one common terminal (the out) and two inputs, one of which is always connected to the output, depending on current events. Termminals are labled, C for Common, NC for Normally Closed, and NO for Normally Open. NC would be where the bypass is connected to allow current to flow when there is no oil pressure (current would flow from NC to C thus allowing the pump to run when you try to start the engine. Once oil pressure comes up enough to trip the pressure switch, current will flow from NO to C, and keep the pump running.
This set up allows the pump to run as long as there is oil pressure and to run ONLY if you are actively trying to start the engine.